Commonly used methods for characterizing mass density of thin films include X-ray reflectivity (XRR) and Rutherford backscattering (RBS). However, there are limitations for both the XRR and RBS methods related to large probe size and sample volume. As such, these methods work well only on full film samples and cannot be used to probe localized device structures of a nanometer scale, such as magnetic writer head devices with complicated topography and nanometer scale sized areas of interest thereon.
Another method, X-ray diffraction (XRD), can probe thin film structure and measure the lattice constant and therefore deduce the mass density if the film composition is known. However, similar to the XRR method which uses X-ray as the probe beam, it is generally impossible to utilize at the nanometer scale for current writer devices. As such, a method for characterizing film density at the nanometer scale device level that addresses these shortcomings is needed.